A model for the distribution of shallow earthquake magnitudes in and around New Zealand is presented. The model comprises 9 onshore and 8 offshore regions, selected for their general tectonic homogeneity. For each region, values of the Gutenberg and Richter seismicity parameters a and b are estimated using seismological, geological and tectonic data. Smooth transitions between regions are achieved using concepts from fuzzy set theory. The model is well-suited to seismic risk computations.